Hilda group

The Hilda group is a group of asteroids that define the outer
edge of the main asteroid belt, about
4 AU from the Sun. These asteroids have become locked into their present orbits by
a gravitational resonance with Jupiter: a Hilda makes exactly three orbits
of the Sun for every two that Jupiter makes. The prototype is 153 Hilda,
discovered in 1875 by Johanna Palisa.